In the prior art, Cupp, U.S. Pat. No. 3,618,044, discloses and claims a method and apparatus for converting binary into ternary recording codes and transforming the ternary symbol strings into a clocked multilevel recording signal and imprinting said recording signal upon a magnetic medium. Cupp, however, is concerned with and processes absolute signal levels rather than signal transitions.
Larkin, U.S. Pat. No. 3,133,274, converts a ternary symbol string into a binary (2-level) write current waveform, which waveform is then used for saturation recording. Further, Larkin uses a synchronous clock and a peak/polarity detector for recovering the saturated recorded code symbols. Central to his invention is the notion of decoding a detected positive peak as a "2", and a negative peak as a "1". In Larkin, the absence of a peak is taken to be a "0". It should be appreciated that, in saturation recording, a negative and positive peak must alternate. Thus, it would not be possible to record and recover a string in Larkin of "2" followed by "2". That is, one could not force two consecutive peaks to both be positive. This is avoided in Larkin by inserting a dummy negative peak in-between the positive peaks corresponding to the "2" symbols. This superflous negative peak will not occur at a code bit time as marked by the clock. Therefore, Larkin discards all such superflous or dummy peaks which were inserted solely to conform to the necessary peak polarity alternation as the detected peaks are decoded into code symbols. However, Larkin ignores the effect of insertion of superflous transitions in the write signal "in-between clock times" which is the shifting of peaks from their expected positions. Peak insertion will increase the detection error unless the clock is slowed down and recording density is lost.